The present invention relates to monopole antennas and, more particularly to a new and improved monopole antenna that radiates an improved radiation pattern and does not require a ground plane.
Recent advances in materials and structural designs have enabled manufacturers of small aircraft to make a greater number of aircraft designs with the use of non-metallic composite materials or fabrics.
In general, antenna for such aircraft can be of a dipole type or monopole type with a ground plane cooperating therewith. An advantage of the monopole type results from the antenna having smaller dimensions. However, in most monopole antennas the ground plane comprises a horizontal metal plate through which coax connections are made and upon which the vertically oriented antenna is mounted. This ground plate does not cause significant technical metallic aircraft problems but raises problems for non-metallic aircraft because of the difficulty in fabricating the ground plate as part of the aircraft.
For these reasons, the dipole antenna is used in many non-metallic aircraft applications. One conventional dipole antenna for such application comprises simply a balun transformer coupled to two strips of one or one and one-half inch wide copper tape extending in opposite directions or forming a V-shaped configuration and supported on a vertical part of the aircraft. The design parameters of these conventional dipole antennas, however, can not be closely configured and are generally unreliable in operation.
Recent improved designs of antenna for non-metallic aircraft include dipole and loop antennas disclosed in copending U.S. patent application Ser. No. 08/371,510 filed Jan. 11, 1995 which discloses such antennas formed of metal clad secured to a dielectric substrate. Said co-pending patent application is owned by the assignee of the present patent application.
A prior monopole antenna Patent that purports to reduce dependence for a ground plane includes U.S. Pat. No. 3,588,903 issued to W. Hampton, on Jun. 28, 1971 which discloses the need for two or more concentric radiator tubes end fed by a coaxial cable. Power to the coaxial cable is purportedly resonant with the upper and lower frequency limits thereby shifting the current lobe away from the base, thereby attempting to maintain near zero current at the radiator base.